# Analysis of Doherty Power Amplifier Matching Assisted by Physics-Based Device Modelling

^{*}

^{†}

## Abstract

**:**

## 1. Introduction

## 2. TCAD Simulation Setup for the Doherty Amplifier Design

## 3. TCAD Simulation of the Main and Auxiliary Stages

- class AB stage (${V}_{\mathrm{GS}}=-3$ V) & $({R}_{\mathrm{test}}={R}_{\mathrm{opt}})$. This represents a conventional class AB stage (used for reference) and also the expected operation of the MAIN amplifier at high power. Hereafter, we refer to this case as “ClassAB”.
- class AB stage (${V}_{\mathrm{GS}}=-3$ V) & $({R}_{\mathrm{test}}=2{R}_{\mathrm{opt}})$. This represents the expected operation of the MAIN amplifier in back-off. Hereafter, we refer to this case as “DohertyAB”.
- class C stage (${V}_{\mathrm{GS}}=-5$ V) & $({R}_{\mathrm{test}}={R}_{\mathrm{opt}})$. This represents the expected operation of the AUX amplifier at high power. Hereafter, we refer to this case as “DohertyC”.

**classC high Z load**curves). It can be seen that the input reflection coefficient in back-off significantly differs from the DohertyC case: the combination of the feedback device capacitance and of the high resistive load pushes ${G}_{\mathrm{in}}$ towards the centre of the Smith Chart. This reduces the mismatch of the class C stage in back-off and limits the gain penalty (see Figure 6, left). On the other hand, the class C stage exhibits a more sharp turn-on, which is beneficial for the Doherty operation, but at a higher output power, which may lead to a later turn-on of the AUX stage.

## 4. TCAD Simulation of the Doherty Amplifier

## 5. Conclusions

## Author Contributions

## Funding

## Data Availability Statement

## Conflicts of Interest

## References

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**Figure 1.**MESFET transcharacteristic (

**left**) and output characteristics (

**right**). The estimated threshold voltage is −3.75 V. Red square: Class AB bias point (10% IDSS) of the MAIN device and the class AB stage with parallel devices. Blue circle: class C bias point of the AUX device.

**Figure 2.**Circuit setup for the single-stage analysis. The resistance ${R}_{\mathrm{test}}$ is set to $2{R}_{\mathrm{opt}}$ or ${R}_{\mathrm{opt}}$ to mimic the operation of the MAIN amplifier in back-off or saturation, respectively. ${R}_{\mathrm{test}}$ is set to ${R}_{\mathrm{DS}}$ or ${R}_{\mathrm{opt}}$ to mimic the operation of the AUX amplifier in back-off or saturation, respectively.

**Figure 3.**Circuit setup for the TCAD Doherty simulation. In TCAD simulations, the embedding circuit is substituted by an equivalent $2\times 2$ impedance matrix coupling the drain ports of the main and auxiliary devices. The mesh for each device includes roughly 3200 nodes.

**Figure 4.**${P}_{\mathrm{out}}$ (

**left**), efficiency and PAE (

**middle**) and power gain (

**right**) for the three cases: classAB, DohertyAB and DohertyC.

**Figure 5.**Left: Input reflection coefficient ${\mathsf{\Gamma}}_{\mathrm{in}}$ for the three cases: classAB, DohertyAB and DohertyC. AB-HPM (class AB–High-Power Match) matches the input port of the class AB at peak power. D-LPM matches the DohertyAB amplifier in back-off and C-HPM matches the input port of the DohertyC at peak power. Right: Class C input reflection coefficient of the DohertyC (dashed line) compared to a class C stage loaded with high impedance (equivalent to ${R}_{\mathrm{DS}}$—dotted line). Red arrow: expected modulation of the AUX amplifier input reflection coefficient in the Doherty amplifier.

**Figure 6.**Transducer gain (

**left**) for classAB, DohertyAB, DohertyC and classC loaded on high impedance. Input return loss for classAB and DohertyAB (

**middle**). Input return loss for DohertyC and classC loaded on high impedance (

**right**). All stages are input matched at peak power.

**Figure 7.**${P}_{\mathrm{in}}-{P}_{\mathrm{out}}$ (

**left**), efficiency (

**right**, red) and PAE (

**right**, black) for HPM-DPA, OPT-DPA and Parallel-PA cases.

**Figure 8.**Input (${\mathsf{\Gamma}}_{\mathrm{in}}$) and load (${\mathsf{\Gamma}}_{\mathrm{L}}$) reflection coefficients seen by the MAIN (

**left**) and AUX (

**right**) stages for HPM-DPA (dotted line) and OPT-DPA (dashed line). Square: Optimum power load. Cross: conjugate of ${Z}_{\mathrm{SM}}$ (

**left**) and ${Z}_{\mathrm{SP}}$ (

**right**) in the HPM-DPA. Circle: conjugate of ${Z}_{\mathrm{SM}}$ (

**left**) and ${Z}_{\mathrm{SP}}$ (

**right**) in the OPT-DPA.

**Figure 9.**Power Gain (

**left**) and Output power of the MAIN and AUX stage separately (

**right**) for HPM-DPA, OPT-DPA and Parallel-PA cases.

**Figure 10.**Input return loss of the MAIN (

**left**) and AUX (

**right**) stage for HPM-DPA, OPT-DPA and Parallel-PA cases.

**Figure 11.**Transducer gain (

**left**), efficiency and PAE (

**right**) for three values of the AUX input phase: $\varphi ={90}^{\circ}$ (solid line); $\varphi ={75}^{\circ}$ (dotted line); $\varphi ={55}^{\circ}$ (dashed line).

**Figure 12.**DPA MAIN (solid) and AUX (dotted) dynamic load lines at the AUX turn-on for the three values of the AUX input phase: $\varphi ={90}^{\circ}$ (

**left**); $\varphi ={75}^{\circ}$ (

**middle**); $\varphi ={55}^{\circ}$ (

**right**). The available input power is the same, the output power is 24.8 dBm (

**left**), 24.3 dBm (

**middle**) and 23.9 dBm (

**right**).

**Figure 13.**Input and load reflection coefficients seen by the MAIN (

**left**) and AUX (

**right**) stages for three values of the AUX input generators: $\varphi ={90}^{\circ}$ (solid line); $\varphi ={75}^{\circ}$ (dotted line); $\varphi ={55}^{\circ}$ (dashed line).

**Figure 14.**DPA-saturated output power (solid line) and peak efficiency (dotted line) as a function of the AUX input phase.

${\mathit{P}}_{\mathbf{out}}$ (dBm) | Eff (%) | PAE (%) | Power Gain (dB) | Gain Compression (dB) | |
---|---|---|---|---|---|

$\mathrm{classAB}$ | 27 | 63 | 54 | 8.5 | 2.3 |

$\mathrm{DohertyAB}$ | 24.7 | 62 | 55 | 8.8 | 2.4 |

$\mathrm{DohertyC}$ | 26.6 | 73 | 55 | 5.9 | N/A |

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**MDPI and ACS Style**

Donati Guerrieri, S.; Catoggio, E.; Bonani, F.
Analysis of Doherty Power Amplifier Matching Assisted by Physics-Based Device Modelling. *Electronics* **2023**, *12*, 2101.
https://doi.org/10.3390/electronics12092101

**AMA Style**

Donati Guerrieri S, Catoggio E, Bonani F.
Analysis of Doherty Power Amplifier Matching Assisted by Physics-Based Device Modelling. *Electronics*. 2023; 12(9):2101.
https://doi.org/10.3390/electronics12092101

**Chicago/Turabian Style**

Donati Guerrieri, Simona, Eva Catoggio, and Fabrizio Bonani.
2023. "Analysis of Doherty Power Amplifier Matching Assisted by Physics-Based Device Modelling" *Electronics* 12, no. 9: 2101.
https://doi.org/10.3390/electronics12092101